The invention relates to a diagnostic lamp for fluorescent excitation of a fluorescible material applied to the teeth.
It is known to make plaque which is not normally visible, i.e. the deposits on the teeth consisting mainly of bacteria and causing diseases of the teeth and gums, easily recognizable by painting a fluorescible material on the teeth so that fluorescent radiation can then be stimulated by means of a suitable lamp. It has been shown that fluorescible materials adhere solely or at least preferably to the plaque, but not to the clean and healthy areas of the teeth and gums. The same is true for those places where tartar has formed due to mineralisation of the plaque or which have already fallen prey to caries. Therefore, these critical or unhealthy parts of the teeth can be made visible and localised in a simple manner by the afore-described inspection, since when illuminated, only these areas flouresce and thus stand out from the other non-fluorescent areas.
A diagnostic lamp for inspecting the teeth, which is constructed in the form of a pocket appliance and is provided with an exchangeable dispenser for a fluorescible material is already known from U.S. Pat. No. 4,195,329 by the same applicant. The following difficulties occurred in the search for improvements to the degree of optical efficiency of this diagnostic lamp, which is preferably operated with the lowest possible power, and in the search for ways of increasing the visible contrast between fluorescent areas and non-fluorescent areas which are solely reflecting areas:
A fluorescible material which is best suited in practice is a fluorescein solution. The spectrum for the stimulation of a typical fluorescein solution with visible light comprises the wave length range of between approximately 450 and 410 nm, i.e. substantially blue light, the absorption maximum in a typical case being 495 nm. The maximum fluorescent radiation emitted is at only slightly higher wave lengths, namely at approximately 525 nm. In order that this fluorescence spectral range and as far as possible the remaining visible light of longer wave lengths are blocked out in a satisfactory manner from the light of the incandescent bulb, a dichroic filter of corresponding dimensions is most suitable, whose transmission curve falls steeply at approximately 500 nm and, for perpendicularly incident light, only allows light to pass therethrough again in the long wave red or infrared range. However, in order that the light strikes the filter substantially at right-angles, one must have a beam of parallel rays, in which case the cross section of this beam of rays should be sufficiently large in order that at least approximately the entire set of teeth or the entire mouth cavity is illuminated upon inspection. However, a substantially larger lamp with a correspondingly more complicated optical arrangement would be necessary to fulfil this requirement.
However, if in order to avoid the use of a parallel beam of rays with a relatively large cross section, one were to use a divergent beam of rays, then, as was ascertained, a dichroic filter would allow all the more light to pass in the visible red range, the greater the angle of incidence of the radiation, i.e. the further the rays from the geometric axis of the beam. For rays striking the filter at an angle of 45.degree., the transmission curve of a dichroic filter once more increases steeply at approximately 650 nm. This has the result that when using a suitable divergent beam of rays, the illuminated area to be inspected appears red in the vicinity of the edge, in which case this reflected red light virtually covers any possible fluorescent radiation and makes the latter invisible, so that a reasonable inspection is impossible.